Chassis-mounted power supplies are known to include external power connectors and wiring harnesses to connect them to device components and printed circuit boards (PCBs). These chassis-mounted supplies are generally complete supplies, including inrush limiting circuitry, EMI filtering, etc., but have the unfortunate consequence of requiring a cable or wiring interface to the printed circuit board.
Similarly, PCB mountable power converters are used that include standard pins to connect to input power provided on a printed circuit board. These devices require high-voltage traces on the printed circuit board to conduct power from an independent AC connector. These supplies also provide almost no inrush current limiting functionality, and may or may not have sufficient EMI filtering. As is well understood, the EMI characteristics of the device in which the power supply is used may be negatively impacted by the use of AC traces or wiring, and the characteristics of the power supply employed. As a consequence the user must provide an external power connector and make the necessary high-voltage connections on the printed circuit board. Also, the user is typically required to provide some form of inrush current limiting circuitry to protect internal fusing and minimize stresses on the circuitry in such supplies. The additional circuitry and components required to use such supplies may also impact safety agency approval and certification.
As a solution to the inherent problems with existing power supplies, the present invention incorporates improved packaging and design, along with specific circuits that are essential to optimize the benefits of an integrated and encapsulated power converter, whereby all components are contained within a common enclosure. Consequently, it has been determined that once the power supplying components are contained within a common enclosure it is highly desirable to encapsulate the entire power supply to provide environmental protection and immunity to dirt, moisture and vibration. The encapsulant also preferably provides a thermally conductive pathway to dissipate the generated heat of the power switching transistors, rectifier and the transformer. Furthermore encapsulation with a material having a high dielectric constant allows the components to be placed in closer proximity, while maintaining requirements relating to safety and certification.
Therefore, it is apparent that an integrated, encapsulated power converter (EPC) that is mounted on-board, provides a solution to a long standing problem, as mentioned above. In a preferred embodiment, the power converter also has a direct connection to the AC line voltage, thereby eliminating the need for AC wiring within the device. However, in order to take full advantage of this solution, specific circuitry limitations must be addressed. For example, encapsulation limits the ability to replace or reset a fuse or similar safety component within the power module. Accordingly, the circuit design of the present invention is specifically designed to limit excessive current and avoid premature component failure.
It is therefore an object of the invention to provide a highly reliable fully integrated power module that controls the in-rush current and associated voltage stress on the bridge rectifier, line fuses and semiconductor switches.
In accordance with an aspect of the present invention, there is provided an electronic power converter, comprising: an encapsulated portion including at least high-voltage electronic circuitry; and an integrated connector for receiving a detachable line cord having at least two wires therein, wherein said power converter is suitable for mounting on a printed circuit board.
In accordance with another aspect of the present invention, there is provided an electronic encapsulated power converter, comprising: a case; an integrated, multi-pin detachable line cord connector accessible through said case; and threaded mounts extending from said case, wherein the threaded mounts are earth grounded internal to the supply and through a line cord, and allow the converter to be rigidly mounted to a circuit board.
In accordance with yet another aspect of the present invention, there is provided an encapsulated power converter having an inrush current limiting circuit, said inrush current limiting circuit, including: a rectifier with a DC return path; a MOSFET switch connected to the DC return path of the bridge rectifier; a capacitor which is slowly charged via a current limited source; where the charge stored on the capacitor is a source of energy to gate the MOSFET; a voltage level detection circuit to maintain the MOSFET switch in an off state until a line voltage reaches a near zero threshold; a resistive charging path to turn the MOSFET switch to an on state once the line voltage reaches the near zero threshold; and a resistive connection to a housekeeping supply of the power converter which maintains the MOSFET switch in the on state.
In accordance with a further aspect of the present invention, there is provided an electronic device, comprising; at least one circuit board located within the device; a cover enclosing the electronic device; and an electronic power converter including fully encapsulated electronic circuitry; and an integrated connector, accessed through an aperture in said cover, for receiving a detachable line cord having at least two wires therein, wherein said power converted is mounted on said circuit board.
The techniques described above are advantageous because they improve the long term reliability and operational characteristics and simplify the overall design of AC powered electronic equipment. As a result of the invention, it is possible to incorporate integrated power supply componentry into a device without the need to handle AC wiring or switching. Moreover, the life cycle of a discrete, encapsulated power supply with integrated AC components has been improved by adding circuitry to safeguard the high failure power components from excessive electrical stress and at the same time protect the user from exposure to potentially lethal AC line voltage.
The present invention will be described in connection with a preferred embodiment, however, it will be understood that there is no intent to limit the invention to the embodiment described. On the contrary, the intent is to cover all alternatives, modifications, and equivalents as may be included within the spirit and scope of the invention as defined by the appended claims.